1. Field of Invention
The present invention relates to automatically engageable and disengageable differential inhibiting devices and more particularly relates to limited slip differential devices utilizing friction disc clutch arrangements and a single sensor for sensing the acceleration of a monitored gear, or related member, and a control for engaging the disc clutch when the acceleration of the monitored gear exceeds a predetermined maximum value. More particularly, this invention relates to an automatically engageable and disengageable limited slip differential for a drive axle which includes a friction disc clutch which will be automatically engaged or disengaged dependent upon ring gear acceleration.
2. Description of the Prior Art
The advantages of a differential inhibiting device such as a limited differential arrangement of the interaxle or final drive of a vehicle are well known. A conventional vehicle differential allows a difference in angular velocity between two driving wheels while turning corners; however, if one of the driving wheels encounters poor traction on a slippery surface, such will tend to cause the wheel to spin and thus limit total driving torque to twice that of the spinning wheel causing the opposite wheel to remain stationary. This operating condition, generally referred to as a "spin out", is encountered when a vehicle has one of its driving wheels bearing on an icy or slippery spot on the roadway, while the other wheels are contacting and/or bearing on a surface having a greater coefficient of friction. Under such circumstances, a relatively low wheel torque will cause the wheel which bears on the slippery surface to spin and a torque equal in magnitude to this low torque will be all the torque available to the wheel on the drive pavement and/or surface of greater coefficient of friction, which will more than likely be insufficient to move the vehicle. Well known means are often provided for automatically reducing or eliminating the normal action of the axle differential.
In conventional types of limited slip differentials employing friction clutch discs the friction discs are generally continuously loaded by compression springs and/or similar conventional force loading apparatus. However, these previous friction clutch devices are usually continuously, operatively engaged, even though the majority of the time such a device is not required. Accordingly, such friction clutch devices are continuously subjected to extreme and detrimental wear which results in frequent repair and replacement thereof. Moreover, these prior art spring biased friction clutches are generally disposed about one or both of the output axle shafts and are operatively positioned in the throat section of the axle housing. Structurally locating the spring biased friction clutch in this manner generally requires an extremely large number of friction discs and a corresponding increase in the spring rate and/or load to effectively achieve reasonable clutching action.
An improved limited slip differential device is described in U.S. Pat. No. 3,448,635, issued Mar. 27, 1967, assigned to the assignee of this application, and hereby incorporated by reference. While the limited slip differential described in U.S. Pat. No. 3,448,635 provided improved mechanical characteristics, the device did require manual actuation by the vehicle operator.
Other differential devices, such as illustrated in U.S. Pat. No. 3,138,970, utilized automatic means to positively lock a differential, or to apply a friction clutch in a limited slip differential device. These devices have not been totally satisfactory as at least two sensors, one for each axle shaft, are usually required. Providing two sensors introduces additional costs, additional circuitry and the like. Further, such devices usually sensed axle rotation and were normally located at the outer ends of the axle housing and were thus more subject to the jolting often experienced by a vehicle axle. U.S. Pat. Nos. 3,473,120; 6,683,219; 3,732,752; 3,845,671 and 3,871,249 are representative of the prior art devices. Also, many of these prior art devices were less than totally satisfactory as they were speed sensitive devices which might lock up the differential, or engage the limited slip clutch discs, during a high speed turn when both wheels were rolling substantially without slippage and full differential action was desired to prevent undue tire wear, excessive stress to the differential mechanism and the like.